The proposed studies will examine (a) the kinetics of entry of lipids and proteins into myelin and myelin subfractions, (b) the subcellular sites of synthesis of these lipids and proteins, and (c) the effects of inhibitors and altered developmental states on myelin assembly. The myelin components to be studied are the galactolipids cerebroside and sulfatide; the choline and ethanolamine phospholipids, the ganglioside GM1; and the basic protein and proteolipid protein of myelin. Double-label isotope experiments will be used extensively. The kinetics of entry of lipids and proteins into myelin will be studied in brain slices with pulse-chase experiments. Inhibitors of protein synthesis and ceramide analogs which perturb galactocerebroside metabolism will be incubated with brain slices to determine their effects on myelin assembly. Subfractions prepared from myelin and Golgi fractions isolated from white matter of calf brain will be characterized to determine whether these membranes are the sites of synthesis of any of the myelin components. Finally, the effects corticosteroid treatment or hypoglycemia in newborn rats on subsequent myelination will be determinnd.